Under a background of social conditions such as an aging society and spreads of a lifestyle-related illness in recent years, needs for an immunological test system with high sensitive and high quantitative property, which enables early detection and early treatment of illness, are increasing. As a candidate of the immunological test system described above, there is given a magnetic biosensor. The magnetic biosensor is a detection system for detecting a target substance in a sample solution by magnetically detecting the magnetic markers locating in a vicinity of a surface of a detection section.
As the magnetic biosensor, there are known a superconducting quantum interference device (SQUID), a hall effect device, a magneto-resistance effect device, a magnetic impedance device, and the like.
In order to achieve a magnetic biosensor with high sensitivity and excellent in the quantitative property, development of a magnetic marker having the following properties is demanded. That is, the magnetic marker is required to have (1) a small size and excellent monodispersity; (2) large saturated magnetization of each of the magnetic markers (magnetic material content is high); and (3) excellent dispersion stability. The property (1) affects an enhancement of the quantitative property of the target substance in the magnetic biosensor. Further, the property (2) affects an enhancement of detection sensitivity of the target substance, and the property (3) affects an enhancement of the quantitative property of the target substance.
However, in many cases, the above-mentioned three properties are in a trade-off relation, thereby being difficult to produce a magnetic marker which fulfills the all properties. Under the above-mentioned background, there is disclosed a magnetic marker including a nonmagnetic substance such as a polymeric compound having a relatively high degree of freedoms of a molecular design and selection, and a magnetic material. For example, Japanese Patent Application Laid-Open No. 2004-099844 discloses a technique of obtaining a magnetic marker by utilizing a miniemulsion polymerization method. Further, in p145 of Preprints of the 14th Polymeric Microspheres Symposium, there is disclosed a technique of obtaining a magnetic marker through utilization of soap-free emulsion polymerization. In addition, Colloid Polymer Science, (2006), No. 284, p1443-p1451 discloses a technique of obtaining a magnetic marker by synthesizing a magnetic material using as a template the gel particle.
However, in the magnetic biosensor applying those magnetic markers, there is a problem in that, in order to achieve a high sensitive detection, magnitude of saturated magnetization is insufficient. It is possible to enhance the saturated magnetization of the magnetic markers by increasing a magnetic material content of each of the magnetic markers. However, by doing so, due to the trade-off relation described above, monodispersity and dispersion stability of the magnetic markers are degraded, and hence the quantitative property of the magnetic biosensor may be impaired.